Radiopaque fluorocarbons (RFC) have achieved greater potential with the recent revolution in diagnostic imaging. Perfluoroctylbromide has been found to be a cancer specific imaging agent in conjunction with computed tomography and conventional radiography. The high concentration of fluorine in RFC should also prove to be ideal for tumor imaging by nuclear magnetic resonance, and the availability of this imaging tool in the near future likely will make it possible to use lower doses of RFC. There is also a need for a blood pool agent such as RFC emulsion for angiographic imaging using techniques such as gaited computerized tomography, computerized scanned projection radiography and digital video subtraction angiography. Emulsions of RFC similar to the emulsions used clinically as synthetic blood remain within the intravascular space for hours. Because these emulsions diffuse slowly from the vascular space, vascular imaging is enhanced, particularly in the kidney. Emulsion technology has been enhanced by the development and practical application of emulsions for parenteral alimentation and synthetic blood. Additional studies are under way for achieving greater emulsion stability and safety. There is also evidence that specific tissue and organ distribution and dwell times are effected significantly by factors such as emulsion charge and particle size. Because the RFC compounds have a longer residence time than conventional X-ray contrast agents, safety studies are more complex and time consuming. The emulsions of RFC are sequestered in macrophage cells. Although the fluorocarbons generally have been considered to be chemically stable, there is evidence they are not biologically inert. Macrophage activation by fluorocarbons has a significant effect on immune properties such as cytotoxity to tumor cells and antimicrobial activity. The immunologic effects of fluorocarbons have been constructive to the organism. Further detailed searches for destructive immunologic effects are an essential part of any safety study. Fluorocarbon-macrophage activation may have therapeutic implications.